Calcium carbonate is used extensively in the paper industry as a filler component in paper. It is a low cost, high brightness filler used to increase sheet brightness and opacity. Its use has increased dramatically in the last decades due to the conversion from acid to alkaline papermaking at paper mills. Both natural and synthetic calcium carbonates are used in the paper industry. Natural carbonate, such as limestone, marble or chalk is ground to a small particle size prior to its use in paper, while synthetic calcium carbonate is manufactured by a precipitation reaction and is therefore called precipitated calcium carbonate (PCC).
Usually, PCC is prepared by introducing CO2 into an aqueous suspension of calcium hydroxide, the so-called milk of limeCa(OH)2+CO2→CaCO3+H2O.
This process has demonstrated the capability to produce PCC with superior opacifying characteristics, PCC is typically superior in opacifying and brightening the sheet, as compared to ground calcium carbonate (so-called GCC). Scalenohedral-shaped precipitated calcium carbonate with a rosette-like aggregate structure has been found to impart high sheet opacity. The carbonation process has also shown flexibility in producing various particle shapes and sizes for various applications as both a paper filler and in paper coatings.
Besides its use in the papermaking industry, precipitated calcium carbonate is also used for various other purposes, e.g. as filler or pigment in the paint industries, and as functional filler for the manufacture of plastic materials, plastisols, sealing compounds, printing inks, rubber, toothpaste, cosmetics, etc.